What is the condition of the suction vapor when an ammonia compressor is operating with -30°F suction temperature and a suction pressure of 8.7 inches of vacuum?

When analyzing the condition of the suction vapor in an ammonia compressor operating at a suction temperature of -30°F and a suction pressure of 8.7 inches of vacuum, it's essential to relate these conditions to the properties of ammonia.

In refrigeration systems, particularly with ammonia, the vapor needs to be evaluated in terms of temperature and pressure to determine if it is superheated, saturated, or sub-cooled. The key point is that at -30°F, the ammonia vapor is actually below its saturation temperature at the given suction pressure.

Given that we are working with a vacuum pressure of 8.7 inches, this indicates that the pressure is significantly lower than atmospheric pressure, and we need to refer to ammonia's phase diagram or pressure-temperature chart to determine the saturation properties at this pressure.

At the suction pressure specified, when we check the saturation properties of ammonia, we find that the saturation temperature corresponding to this vacuum pressure is higher than -30°F. Consequently, since the actual suction temperature is lower than the saturation temperature, it indicates that the ammonia is in a superheated state, rather than saturated or sub-cooled.

The specific answer reflects that the suction vapor is superheated, which means it is operating above the saturation temperature at that specific pressure